There is known a capacitive acceleration sensor detecting acceleration acting on a substance by detecting change in capacitance between electrodes (between a fixed electrode and a movable electrode) opposed to each other.
A gyro sensor is utilized for applications such as image stabilization in a video camera or a still camera, position detection in a car navigation system, motion detection in a robot or a gaming machine and the like. An example of the gyro sensor has vibrators driven in respective axial directions one by one for three axes (an X-axis, a Y-axis and a Z-axis) orthogonal orthogonal to one another in a three-directional space, for example. The gyro sensor detects angular velocities acting around the respective axes through Coriolis force acting on the respective vibrators when the sensor inclines. There is also known a gyro sensor detecting angular velocities as to three axes with one rotator, dissimilarly thereto.
For example, the so-called seesaw type is known as a structure of a capacitive acceleration sensor. A seesaw acceleration sensor has an oxide film formed on a semiconductor substrate, a fixed electrode formed on the oxide film and movable electrodes separatingly provided above the fixed electrode to be opposed to the fixed electrode, as a structure detecting acceleration acting in a Z-axis direction, for example. When acceleration acts on the acceleration sensor in the Z-axis direction, the pair of movable electrodes vibrate to alternately vertically move in a direction approaching the fixed electrode and a direction separating therefrom along the Z-axis direction, as if the same constitute a seesaw. The acceleration sensor detects the acceleration in the Z-axis direction by detecting change in capacitance between the movable electrodes and the fixed electrode.
The aforementioned seesaw acceleration sensor is prepared by a technique, such as epitaxial growth, CMP (Chemical Mechanical Polishing), sacrificial layer etching or the like, for example, employed in preparation of an MEMS (Micro Electro Mechanical Systems) device.
More specifically, the oxide film and a sacrificial layer are successively formed on the semiconductor substrate, and an opening of the same pattern as the fixed electrode is formed in the sacrificial layer, for example. Further, a polysilicon layer is formed on the sacrificial layer to fill up the opening, and polysilicon other than the polysilicon layer in the opening is removed by CMP. Thus, the polysilicon layer in the opening is formed as the fixed electrode. Thereafter another sacrificial layer is further formed to cover the fixed electrode, and the sacrificial layer is patterned, so that openings for growing the movable electrodes are formed. Then, an epitaxial layer is formed on the sacrificial layer by epitaxially growing polysilicon from the opening. Thereafter a through-hole reaching the sacrificial layers from the surface of the epitaxial layer is formed. Then, all sacrificial layers are etched through the through-hole. Thus, the sacrificial layers between the movable electrodes and the fixed electrode are removed, and the movable electrodes in a state floating above the fixed electrode are formed.
In a method for manufacturing a capacitive gyro sensor, on the other hand, an oxide film and a sacrificial layer are successively formed on a semiconductor substrate, and an opening of the same pattern as a lower electrode is formed in the sacrificial layer, for example. Further, a polysilicon layer is formed on the sacrificial layer to fill up the opening, and polysilicon other than the polysilicon layer in the opening is removed by CMP. Thus, the polysilicon layer in the opening is formed as the lower electrode. Thereafter another sacrificial layer is further formed to cover the lower electrode, and the sacrificial layer is patterned, so that openings for growing a fixed electrode and a movable electrode are formed. Then, an epitaxial layer is formed on the sacrificial layer by epitaxially growing polysilicon from the openings. Thereafter a through-hole reaching the sacrificial layers from the surface of the epitaxial layer is formed, whereby the fixed electrode and the movable electrode isolated from one another are formed. Further, all sacrificial layers are etched through the through-hole. Thus, the sacrificial layers between the movable electrode and the lower electrode are removed, and the movable electrode enters a state floating with respect to the lower electrode.